This invention relates to an oblique edged cutting tool provided with a shank portion to a front end of which a flat cutting tip of an indexable throw-away type having an outer configuration radially symmetrical about its geometric center is detachably attached.
In the art of this field, a work is generally cut to obtain a finely machined surface by a cemented carbide cutting tool with high speed-minute feed cutting amount or by a high speed steel tool such as a spring tool with low speed-high feed cutting, and in a rare case, an oblique edged tool is utilized at relatively high speed and with relatively high feed cutting amount as shown in FIGS. 1 and 2.
In FIGS. 1 and 2, the oblique edged tool 1 is generally made of a high speed steel and the cutting edge of the tool is integrally formed with a holder 3, which is referred to herein as a holder or shank of the tool. The inclination .alpha. of the cutting edge is usually selected in a range of 45.degree..about.70.degree..
FIG. 3 is a perspective view showing cutting condition in use of the oblique edged tool 1 shown in FIGS. 1 and 2, in which the oblique edged tool 1 which is fed at a feeding amount f with respect to a work 4 rotating with the revolution numbers N performs a cutting operation in contact with a point P of the cutting edge positioned in the same level of an axis O-O' of the work. In FIG. 3, the inclination i is determined by a line m which is the extension of the cutting edge of the oblique edged tool 1 and a line l normal to a cutting velocity direction V (hereinafter may be called merely cutting direction) at the point P of the cutting edge, and in a usual cutting operation in use of a lathe, the direction of the line l substantially accords with the feeding direction of the tool.
However, with the oblique edged tool 1 of the type described above, it is required to regrind the cutting edge 2 every time the cutting edge 2 wears, and after the cutting edge is reground several times, it is necessary to finally dispose of the holder 3 itself, which is not economical.
An oblique edged tool 5 as shown in FIG. 4 has been proposed for obviating the disadvantages described above, in which a tip 6 provided with a cutting edge 7 is detachably fitted to the holder 3 through a keep member 9. Although the tip 6 adapted for the oblique edged tool 5 is provided with two or more cutting edges 7, even a specifically made rectangular tip 6 can provide only four cutting edges 7 defined by the longitudinal four edges of the rectangular tip 6. For this reason, it is required to provide a tip having a lot of cutting edges for the purposes of reducing tip exchanging times and using economically cutting edges. However, in comparison with a non-oblique edged tool with an indexable throw-away type standard tip (a tip made in accordance with ISO, International Organization for Standardization, called hereinafter merely a standard tip), the oblique edged tool 5 with the specifically made rectangular tip 6 seems at a glance to have a long cutting edge 7 contacting the work, so that the application of indexable throw-away type standard tips widely used in tip manufacturing makers to an oblique edged tool is not considered up to today's standard. Moreover, the specifically made rectangular tip 6 can be manufactured from a limited number of substances and is not economical in comparison with the standard tip. Furthermore, the keep member 9 for keeping the tip 6 to the holder 3 projects over the holder surface, so that it is difficult for an operator to observe the cutting edge 7 during the cutting operation. In addition, when the bolt 8 is excessively rotated, there is a fear of falling down the keep member 9, thus adversely affecting the cutting operation.
In another aspect of the prior art of cutting tool having a rod-like shank portion to a front end of which a cutting tip made of a cemented carbide or ceramics is attached has widely been used for a various kinds of machine tools such as a lathe, boring machine and a shaping machine. In a well-known art as shown in FIGS. 5 and 6, a tip 102 is fixed by using a pin or lever, to the front end of a shank 101 of a cutting tool. FIG. 5 shows a cutting condition in which an outer peripheral surface of a rod-like work 103 is cut and FIG. 6 also shows a cutting condition in which an end surface of a disc-like work 103 is cut. In FIGS. 5 and 6, a letter N designates a rotating direction of the work 103 and a letter f designates a feeding direction of a cutting tool. In the use of a cutting tool of the type shown in FIG. 5 or 6, a work is cut by a nose portion 104 between a front edge and side edges of the tip 102, so that it was likely to damage or wear the nose portion 104, and moreover, in some cases, the tip 102 is disposed of without utilizing a portion of the tip other than the nose, thus being not economical. In addition, the nose portion 104 is designed to have a relatively small radius for preventing undesirable chatter vibrations at the cutting time. For this reason, when the feeding amount of the cutting tool increases, the surface of the work is roughly finished or machined and when the feeding amount decreases, the cutting efficiency is lowered. Generally, degree of finishing roughness H.sub.o of the work 103 is represented by the following equation, EQU H.sub.o =F.sup.2 /8r
where f is a feeding amount per one rotation of the work and r is radius of the nose portion.
Furthermore, in a case where the tip 102 is made of a material having high hardness such as cemented carbide, ceramics or cermet, a rake angle cannot be set to be large, so that the cutting condition is degraded and the cutting resistance increases thereby not to perform a fine cut-in operation. The increasing of the cutting resistance generates a high cutting heat which results in undesirable thermal expansion of the cutting tool or the work thereby not to attain a high working performance. In addition, in a case where the work is cut intermittently, the nose portion of the tip is likely damaged and many burrs are formed.